The present invention relates to a drive control apparatus and a drive control method for controlling the drive of an inductive load. Specifically, the invention relates to a driver control apparatus and a drive control method, which are applied preferably for controlling the drive of an inductive load such as a solenoid actuator used in automatic transmissions for automobiles. Hereinafter, the drive control apparatus for controlling the drive of an inductive load will be referred to simply as the “drive control apparatus”. Also, the drive control method for controlling the drive of an inductive load will be referred to simply as the “drive control method”.
In driving an inductive load such as the solenoid actuator used in automatic transmissions for automobiles, the current flowing through the inductive load is controlled by pulse width modulation (hereinafter referred to as “PWM”).
FIG. 21 is a block diagram briefly describing a closed loop control system, to which a conventional drive control apparatus is applied.
In FIG. 21, driver circuit 13 that drives inductive load 15 is connected to a first end of inductive load 15 such as a linear solenoid. Current detecting resistor 17 is connected in series to a second end of inductive load 15. Drive control circuit 102 that conducts PWM control by analog data processing is disposed in a front stage of driver circuit 13. D/A converter 101 is disposed in a front stage of drive control circuit 102.
Average current detecting circuit 14 that detects an average value of the current flowing through inductive load 15 is connected between the first and second ends of current detecting resistor 17. An output from average current detecting circuit 14 is connected to drive control circuit 102.
A current value control data FC that indicates the reference value of the current flowing through inductive load 15 is converted to an analog data in D/A converter 101. Then, the converted analog data is fed to drive control circuit 102. Current If that flows through inductance L of inductive load 15 flows through current detecting resistor 17. The average value IAVR of current If flowing through inductive load 15 is detected by the average current detecting circuit 14 and fed to drive control circuit 102. (Hereinafter, current If flowing through inductive load 15 will be referred to simply as “current If”)
Drive control circuit 102 generates a PWM signal, which makes the average value IAVR of current If coincide with the reference value indicated by the current value control data FC, to control the ON and OFF of a switching device in driver circuit 13, thereby further conducting the PWM control over current If.
FIG. 22 is a block diagram briefly describing another closed loop control system, to which a conventional drive control apparatus is applied.
In FIG. 22, driver circuit 13 that drives inductive load 15 is connected to the first end of inductive load 15 and current detecting resistor 17 is connected in series to the second end of inductive load 15. Drive control circuit 112 that conducts PWM control by digital data processing is disposed in the front stage of driver circuit 13.
Average current detecting circuit 114 is connected between the first and second ends of current detecting resistor 17. The output from average current detecting circuit 114 is connected to drive control circuit 112 via A/D converter 111.
The current value control data FC, which indicates the reference value of the current flowing through inductive load 15, is fed to drive control circuit 112. Current If that flows through inductance L of inductive load 15 flows through current detecting resistor 17. The average value IAVR of current If is detected by average current detecting circuit 114. The average value IAVR is converted to a digital data by A/D converter 111 and fed to drive control circuit 112.
Drive control circuit 112 generates a PWM signal that makes the average value IAVR of current If coincide with the reference value indicated by the current value control data FC to control the ON and OFF of a switching device in driver circuit 13, thereby further conducting the PWM control of current If.
FIG. 23 is a timing chart describing the waveform of current If that is made to flow through inductive load 15 by the PWM control conducted by the conventional drive control apparatus.
As described in FIG. 23, current If is controlled to increase when a PWM signal level is high and to decrease when the PWM signal level is low so that the average value IAVR of current If may coincide with the reference value indicated by the current value control data FC.
The states of the PWM signal (on the high level or on the low level) are determined by the functions of a switching device used in driver circuit 13. In the example described above with reference to FIG. 23, it is assumed that the switching device shifts to the OFF-state thereof when the PWM signal level is low.
By controlling the ON and OFF of the switching device in driver circuit 13, a current ripple, the maximum value of which is a peak current IH and the minimum value of which is a bottom current IL, is caused on current If. The period T of the PWM signal for controlling an automatic transmission for automobiles is set so that the plunger of a linear solenoid is provided with micro-vibrations and the sliding resistance of the linear solenoid may be minimized.
A current ripple amount (IH−IL) is set within the specifications of the detectable current range of average current detecting circuit 14 so as not to cause any error in the average current value IAVR detected by average current detecting circuit 14.
In controlling currents If flowing through inductive loads 15 and exhibiting different characteristics, current If flowing through any of inductive loads 15 may be sometimes outside the detectable current range of average current detecting circuit 14, since the peak current IH and the bottom current IL change.
FIG. 24 is a timing chart describing the waveforms of currents If flowing through inductive loads 15 exhibiting different characteristics, during the PWM control conducted by the conventional drive control apparatus.
As inductance L of inductive load 15 becomes small in FIG. 24, the current ripple amount (IH−IL) of current If′ flowing through inductive load 15 increases. If the detectable current range of average current detecting circuit 14 is set corresponding to the normal current ripple amount (IH−IL) of current If, the current ripple amount (IH−IL) of current If′ will be outside the detectable current range of average current detecting circuit 14.
For controlling currents If flowing through inductive loads 15 exhibiting different characteristics, average current detecting circuits 14 having the respective detectable current ranges are prepared according to the characteristics of inductive loads 15. Alternatively, average current detecting circuit 14 having a detectable current range corresponding to a possible peak current IH and a possible bottom current IL is prepared.
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2007-40361, Counterpart: WO 2007015485) discloses a method for obtaining dither frequencies for various voltages applied to a solenoid valve from a map by using the driving currents of the solenoid valve as parameters. The method disclosed in the Patent Document 1 facilitates reductions of the hysteresis motion of the solenoid valve and the abrasion of a movable part.
Patent Document 2 (Japanese Unexamined Patent Application Publication No. 11-159652) discloses a method for changing a control target (reference value) and a dither frequency preset in a pulse width modulation circuit to automatically change the dither frequency in addition to the control target for a solenoid proportional control valve. The method disclosed in the Patent Document 2 realizes the variable dither frequency and the control of the solenoid proportional control valve with low costs.
FIG. 25 is a timing chart describing the waveform of current If flowing through inductive load 15 and controlled by a PWM signal with a dither signal from the conventional drive control apparatus.
In FIG. 25, a dither signal having the frequency higher than the frequency of a PWM signal is superposed onto the PWM signal. Here, the period of the dither signal is represented by Δt. By the superposition, the ON-period and OFF-period of the PWM signal are subdivided into short periods. Further, by setting an ON/OFF time ration R in the subdivided short periods, the peak current IH and the bottom current IL are adjusted. In detail, even in the ON-period of the PWM signal, current If decreases for the time period Δt·(1−R), for which the switching device is OFF, in the subdivided short period Δt. Even in the OFF period of the PWM signal, current If increases for the time period Δt (1−R), for which the switching device is ON, in the subdivided short period Δt. Therefore, the differences caused in the ripple amount (IH−IL) of current If can be negated by changing the ratio R of the dither signal corresponding to the differences of the characteristics of inductive loads 15. Even when the characteristics of inductive loads 15 are different, the current ripple amounts (IH−IL) can be controlled within the detectable current range of average current detecting circuit 14. When the time ratio R is set at 1, the current ripple amount (IH−IL) shows the maximum.
In preparing average current detecting circuits 14 wherein the respective detectable current ranges thereof are different from each other, considering the characteristics of inductive loads 15, a specific circuit design will be necessary for every inductive load 15 and the man-hours necessary for designing and the costs necessary for development will increase.
If preparing average current detecting circuit 14 having a detectable current range corresponding to possible ranges of the peak current IH and bottom current IL, the specifications for the detectable current range of average current detecting circuit 14 will be determined uniformly. Therefore, inductive load 15 outside the specifications will be unusable. Moreover, if inductive load 15, wherein the current ripple amount (IH−IL) thereof is small, is used, only a small part of the detectable current range of average current detecting circuit 14 will be used, leaving a large part of the circuit useless.
For controlling the current ripple amount (IH−IL) within the detectable current range of average current detecting circuit 14 by the method for adding a dither signal to a PWM signal, it is necessary to change the dither signal time ratio R corresponding to the differences in characteristics of inductive loads 15. Therefore, it is necessary to prepare an IC for every inductive load 15, thereby increasing the manufacturing costs.
In view of the foregoing, it would be desirable to obviate the problems described above. It would be also desirable to provide a drive control apparatus for controlling the drive of an inductive load on the same circuit to reduce the sliding resistance of a linear solenoid and change the current ripple amount such that the changed current ripple amount is suited for the detectable range of the current flowing through the inductive load. It would be further desirable to provide a drive control method for controlling the drive of an inductive load on a same circuit to reduce the sliding resistance of a linear solenoid and change the current ripple amount such that the changed current ripple amount is suited for the detectable range of the current flowing through the inductive load.
Further objects and advantages of the invention will be apparent from the following description of the invention.